[teambayern]

I know enough to know that an amp is necessary to get the most out of a good pair of headphones, particularly those with high impedance.  But I don't know why.  I listen to SR225s at work with a Fiio E7 (mostly for the DAC) and am looking to get some HE-400s as my next set, another low impedance headphone.  People say to get the Schiit stack or similar DAC/amp because they need it to shine.  I've got the budget for a Schiit stack, but here's the rub:  even with the weak amp on the E7, I find myself listening at really low volumes (between 10-15 usually).  That's loud enough for me, I find you get used to whatever volume you have it on anyway, and I'd like to preserve my hearing for (hopefully) a long life of listening to headphones for a good chunk of time each day.  
 
So given that these headphones don't require much power to drive, and i'm barely taxing the weak amp on the E7 as it is, is there any value in getting the Schiit stack or comparable amp/DAC?  What is it about a good amp that improves the SQ, where volume is not a factor, and how much of a difference am I likely to notice (5%, 10%, 25%, holy **** it's a new headphone)?

 

[ProtegeManiac]

  I know enough to know that an amp is necessary to get the most out of a good pair of headphones, particularly those with high impedance.  But I don't know why.  I listen to SR225s at work with a Fiio E7 (mostly for the DAC) and am looking to get some HE-400s as my next set, another low impedance headphone.  People say to get the Schiit stack or similar DAC/amp because they need it to shine.  I've got the budget for a Schiit stack, but here's the rub:  even with the weak amp on the E7, I find myself listening at really low volumes (between 10-15 usually).  That's loud enough for me, I find you get used to whatever volume you have it on anyway, and I'd like to preserve my hearing for (hopefully) a long life of listening to headphones for a good chunk of time each day.  
 
So given that these headphones don't require much power to drive, and i'm barely taxing the weak amp on the E7 as it is, is there any value in getting the Schiit stack or comparable amp/DAC?  What is it about a good amp that improves the SQ, where volume is not a factor, and how much of a difference am I likely to notice (5%, 10%, 25%, holy **** it's a new headphone)?

 

Impedance isn't that much of a determinant for whether a headphone needs a separate amplifier (from a mainstream device or not) - what is more important is sensitivity, or efficiency. In layman's terms they're effectively the same thing, but as engineering terms the math is different - one is for watts and the other is for voltage. That said, while sensitivity is the primary concern, impedance still comes second. Too low, like, below 32ohms, and you'll likely run into an impedance mismatch as some audio chips - particularly older integrated audio chips and even more modern headphone driver chips (like in the Fiio K5, except their engineers managed to make a circuit that keeps it stable at a low output impedance) - have a high output impedance. If you're at considerably less than a 1:8 output to load impedance ratio, damping factor starts to decrease and you get an EQ effect on the bass (which isn't always boosting it - my integrated amplifier made my SR225 sound like a tin can). Too high impedance, and you drive the audio chip into distortion. The iPod for example is rated for 5mW at 32ohms, and power decreases as impedance increases, and the HD600 sounds like even the instruments have a blocked sinus (my iPad2 and Note3 are a huge improvement over the iPod though).

 

Back to efficiency and your headphones. The Grados are rated at around 105dB/1mW for the e-series, and AFAIK in the 98dB to 100dB-ish range for the i-series. The HE400i are at 93dB/1mW. Note that gain affects how loud they'll actually be as well, so don't assume that, given a smartphone audio chip that makes 5mW at 32ohms at acceptable distortion levels, you can get 105dB at 1/5 and 93dB at roughly 1/3 of max setting. Also, whatever the current output level is, going 3dB louder necessitates doubling the input power, as the graph relationship between input power and actual output is logarithmic rather than linear.

 

Basically what I'm getting at is that the HE400i will need an amplifier to sound good without (much) distortion. However in your case if you're listening at really low volume levels (ie assuming that 10-15 is out of 100 points of adjustment on the E7's attenuator) with the SR225, and that includes the higher audible ambient noise because it's a Grado (ie the sensitivity of Grados is practically canceled out by the lack of isolation), then you probably will not get the E7 to a point where the distortion is easily audible. 

 

In terms of how much difference you'll hear, that depends on the actual loudness. If you're listening at very, very low output levels, then unless you're comparing headphones with extremely different response curves to the point that one is really skewed (ie too much too little bass or treble), The problem however is that the question here is are you actually listening at a very low output level, or is the SR225's sensitivity so high that you're actually listening at a loud enough level that if the E7 was driving both, it might get to a distortion level that would compromise what the HE400i actually sounds like? Note for example how some people claim the HD6x0 are somewhat "lazy" or "too laid back" vs Grados, but when driven by an amp with sufficient voltage output with not a lot of distortion, it can have more of that "popping out"/"eye popping" dynamics that a Grado can have out of a decent mainstream device like a tablet, which by that point is already running out of steam. An amplifier that can run both headphones with very low distortion and listening at a loud enough level can mean the difference between how different each headphone sounds like and in a good way.

 

A quick test that you can do is download an SPL app for your smartphone, and then run with the phone resting on the outer earpad to roughly estimate the the posiiton of your outer ear. This isn't as accurate as a real SPL meter much less a mannequin head with a mic inside it that simulates actually wearing a headphone, but we're just getting a ballpark SPL figure here, not measurements. If you hit at least 70dB, you're not actually listening at a very low volume (my HD600 at the level I use when cranked up for my favorite tracks registers 78dB). 

 

Alternately, why not get the HE400S? It's rated for 98dB sensitivity - that 5dB of difference is a heck of a lot. And while it might be 22ohms, the E7 has a low enough output impedance that this isn't going to be a problem. Coupled with slightly better isolation than the Grados, unless you were listening in a very quiet environment with those, the HE400S might not even use a higher volume setting on the E7. I've seen the response graph on it though and the curve is less HE400i, which is ruler flat from 1000hz down to 10hz and more like a few other dynamic headphones with an upper bass hump and then rolls off earlier than headphones like the HE400i, LCD-x series, etc.

 

If what you're really after is long session wearing comfort than actual curiosity about the sound and you're otherwise happy with the Grado sound, I'd much rather suggest you check out the Headphile mods on Grados. Specifically, the C-Pad and the Vixen. The C-Pad is basically a headphone earpad adapter that allows mounting a Beyerdynamic earpad onto the Grado, except now you'll see wood grain on the adapter so you might want to spend on wood cups and chambers (alternately, you can make one out of plastic if you can access a 3D scanner and printer, just look up how the C-Pad works). If you can save up more cash look into the Vixen - it's basically a Beyerdynamic headband and earpads with custom wood stain earcups that have Grado drivers mounted on them. These use the SR325 and up drivers though so a good strategy would be to wait around for a used RS2 or RS1 and then have it converted into the Vixen.

 

[teambayern]

Wow, really thoughtful and thorough post, thanks so much.  This clarifies a lot.  To answer a few of your questions --
 
1.  I suspect you're right that the volume is low, but not terribly so.  It sounds about even to an iPhone at half volume with 32 ohm ear buds, for example.  
 
2.  You're also right that I am considering the HE-400S, not 400i, so perhaps the E7 will work.  Happy to shell out for something like the Schiit if it will make a difference, and sounds like it will, but perhaps not mind blowing at the volumes i'm listening at.  The description below is helpful.
 
3.  I also appreciate the suggestion for different cups for the grados.  I may do that, but as you suspected, I am curious about the sounds of the HE-400s as well.

 

[ProtegeManiac]

 
2.  You're also right that I am considering the HE-400S, not 400i, so perhaps the E7 will work.  Happy to shell out for something like the Schiit if it will make a difference, and sounds like it will, but perhaps not mind blowing at the volumes i'm listening at.  The description below is helpful.
 
3.  I also appreciate the suggestion for different cups for the grados.  I may do that, but as you suspected, I am curious about the sounds of the HE-400s as well.
 

 

You wrote the "s" in lower case so I thought it was more like in plural form. In any case, that's going to be an easier load on the E7 - given the impedance isn't going to be an issue and the sensitivity is considerably higher, and apart from how the E7 has a default distortion profile (it just makes everything warmer, not so much that it's getting close to clipping), what you'll hear for the most part is what the HE400S sounds like. The Schiit stack will likely be clearer and cleaner, and hard bass/lower midrange hits (kick drum, toms) more prominent, but I wouldn't assume it's going to be anywhere close to being an unbelievable improvement for $200 (non-Uber) to $300 (Uber versions).
 
 

 
1.  I suspect you're right that the volume is low, but not terribly so.  It sounds about even to an iPhone at half volume with 32 ohm ear buds, for example.  

 

That still doesn't get me a good idea on how loud it goes - with my old SGS3 stock headset (tried it on an iPhone4), CX300, and M6P, as well as my current ASG-1.3 and VSD3S, I'm already deaf by that point, unless it's a classical music recording that has a proper low gain (but then if it's the 1812 Overture those cannons can still hurt). Not that I'd get that close anyway because on anything but classical music the distortion is already bad on my SGS3,  clean but painfully loud on my Note3 and iPhones (plus the iPad) at just 1/3.